1. Field of the Invention
The present invention relates to a knee protecting airbag device in which an airbag to be expanded and inflated by admitting an inflating gas can protect the knees of a passenger such as a driver or a person seated on a passenger's seat.
2. Description of the Related Art
In the prior art, a device for protecting the knees of a driver is disclosed in JP-A-8-80797. In this knee protecting airbag device, the airbag is housed in the lower portion of the lower cover of the dash board. When an inflating gas flows in, the airbag is expanded and inflated while rising to protect the shanks and knees of the driver.
In the knee protecting airbag device, however, the airbag is expanded and inflated while rising. Therefore, the upper end of the airbag may deviate to the left and right, when the airbag is completely expanded and inflated. If the deviation is larger, the airbag may fail to receive the knees of the driver moving relatively forward, properly. As a result, there is room for improving the proper arrangement of the completely expanded and inflated airbag properly on the front side of the knees of the driver.
Moreover, the knee protecting airbag device thus constructed has room for improvement, in case the clearance between the knees of the passenger and the vehicular body side member in front of the knees is narrow, in that the airbag folded and housed on the front side of the knees of the passenger is protruded rearward of the vehicle from the housed portion and smoothly expanded and inflated upward with the inflating gas coming from the inflator.
Another knee protecting airbag device is disclosed in JP-A-9-123862. In this knee protecting airbag device, the airbag can be expanded and inflated to hold the column cover covering the steering column on the two sides thereby to prevent the upper end of the airbag from deviating to the left and right.
In the knee protecting airbag device disclosed, however, when the airbag is expanded and inflated, the vehicular rear side of the column cover itself is exposed to the driver. Therefore, the knee protecting airbag device to be activated for a front collision of the vehicle has room for protecting the knees of the driver against the column cover.
In the knee protecting airbag device disclosed, on the other hand, the airbag is constructed to hold the column cover. This airbag device cannot be mounted on the front side of the passenger seated on the passenger's seat, because the column cover is not on the front side of that passenger.
Moreover, the knee protecting airbag device of this kind is required to have its airbag arranged smoothly between the member on the vehicular body side such as the column cover and the knees of the passenger while being freed from the interference with the passenger by suppressing not only the transverse deviation in the vicinity of the upper end of the completely inflated airbag but also the deviation to the passenger side or rearward of the vehicle.
Still another device for protecting the knees of a passenger such as a driver is disclosed in JP-A-10-315894. This knee protecting airbag device includes: an airbag folded in expandable and inflatable manners on the front side of the knees of the seated passenger; an inflator for feeding an inflating gas to the airbag; and a case for housing and holding the folded airbag and the inflator. And, the inflator is of the column-shaped cylinder type to be housed in the airbag and is arranged to have its axis in the transverse direction of the vehicle.
However, the following points are left unsolved, in case the inflator is exemplified by the hybrid type in which the gas discharge ports for discharging the inflating gas are arranged at the axial end portion. In short, the inflator housed in the airbag is arranged to have its gas discharge ports on one transverse edge side of the case. And, the inflating gas discharged from the gas discharge ports flows out into the airbag while being concentrated on the one transverse edge side of the case. As a result, the airbag is protruded from the one vehicular transverse edge side in a case opening so that the airbag may neither be quickly protruded from the case opening and nor be smoothly expanded and inflated.
In the knee protecting airbag device of this kind, moreover, the distance from the column cover or instrument panel (or dash board) to the knees of the passenger is set to a small value when the passenger is seated. Therefore, the airbag to be used in the knee protecting airbag device of this kind is set to have a small capacity as a thin, general sheet shape when it is completely inflated, so that it may be easily expanded and inflated between an obstacle such as the column cover or the dash board and the knees. However, a longer or shorter time difference usually occurs from the start of inflow of the inflating gas to the catch of the passenger's knees by the airbag. In order to protect the knees of the passenger properly with the airbag, therefore, the airbag is desired to keep a high internal pressure even when a predetermined time elapsed after the start of the inflow.
Another device for protecting the knee of the passenger such as a driver is disclosed in JP-A-9-123857. This knee protecting airbag device includes: an airbag folded in an expandable and inflatable manner on the lower side of the front of the knees of a seated passenger; an inflator for feeding an inflating gas to the airbag; and a case for housing and holding the folded airbag and the inflator.
If the airbag device is activated by a front collision of the vehicle, the airbag admits the inflating gas from the inflator so that it is expanded and inflated to protrude and rise rearward of the vehicle from the vehicular rear side opening in the case thereby to protect the knees of the passenger moving forward.
At this time when the flow of the inflating gas is active, the upper end side of the airbag protruded from the case is kept at an upper position by the gas flow so that the airbag can protect the knees properly even if the passenger moves forward.
If, however, the passenger moves forward with a more delay than the ordinary one when the feed of the inflating gas from the inflator is reduced or terminated and stopped and in a state in which the flow of the inflating gas stops, the upper end portion of the airbag may be inclined downward by the weight itself of the airbag even if the internal pressure of the airbag is sufficient. If the upper end portion of the airbag falls down, moreover, the airbag cannot protect the knees of the passenger moving forward with the delay, properly.